Plasma Aluminum-Graphite Composite

A&A Coatings material was specifically developed to provide a plasma sprayed, abradable clearance control coating for gas turbine engines with titanium alloy, and possibly aluminum alloy rotors operating at 315-425°C (600-800°F).

Material Powder Characteristics

Typical Composition: Aluminum 40.0%
Graphite 45.5%
Silicon 5.5%
Organic Binder 9.0%
Typical Size Range: -100 mesh +15 microns
(-150 +15 microns)

Physical Properties of Coating

Surface Texture As-Sprayed
(microinches aa):
700-800
Finish, As-Machined (microinches aa): 100-200
Coating Macrohardness: R15y 55-80
Density (g/cc): 2.0
Coating Weight (lb/ft2/.001″): .10
Thickness Limitation None Apparent

Hardness

A&A Coatings Plasma Sprayed Aluminum-Graphite Composite is sensitive to overaging as is evidenced by a decrease in coating hardness. For example, aging studies show that this aluminum alloy follows a parabolic growth rate concerning the precipitation and growth of the finely dispersed silicon, and is more time than temperature dependent. Hardness decreases can be expected after exposure of several hours at 315°C (600°F). Despite this aging tendency, lower hardness does not reflect an inferior coating.

Surface Preparation

Clean substrate. Severe oxidation must be removed, grit blasting is recommended. Preheat to 95°C (200°F) to prevent formation of condensate.

Finishing

The recommended method for finishing coatings of Aluminum-Graphite Composite is by machining with a single point carbide tool.

Coatings should not be ground. The pressure and heat generated by grinding will compress the coating and alter its properties.

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